1. Field of the Invention
The present invention relates to optical devices, specifically range finders, and particularly to range finders in which a projector directs light onto an object and a number of independent light receiving elements are able to produce outputs corresponding to imaging positions on the light receiving elements so as to measure the distance to the object.
2. Description of the Prior Art
U.S. Pat. No. 3,820,129 discloses the basic arrangement of such type of range finder. In this patent, a bridge circuit detects the difference in outputs of two light receiving elements and this difference is used as a distance signal. However, this arrangement suffers from the fact that the reflection factor of the object whose distance is being measured can vary the difference in outputs of the elements. This prevents an accurate range finding indication. Also, this patent discloses projecting light being received through a filter for eliminating the influence of external light. However, such a method cannot completely eliminate external light. Hence, the outputs of the light receiving elements will be influenced by the ambient light, and could thus result in erroneous distance outputs.